Physics for Scientists and Engineers 9ed. Concept Question Bank
A baseball and a basketball, having the same mass, are dropped through air from rest such that their bottoms are initially at the same height above the ground, on the order of 1 m or more. Which one strikes the ground first? the baseball the basketball both strike the ground at the same time
The basketball, having a larger cross-sectional area, will have a larger force due to air resistance than the baseball. This will result in a smaller net force in the downward direction and a smaller downward acceleration.
an astronaut outside a spaceship hammers a loose rivet back in place, what happens to the astronaut as he swings the hammer
he moves towards the spaceship as he pulls the hammer back and moves away from it as he swings the hammer forward
the object shown below has mass m and velocity v, the direction of its angular momentum vector with respect ot an axis perpendicular to the page through point o is
into the page
If a car is traveling eastward and slowing down, what is the direction of the force on the car that causes it to slow down? eastward westward neither of these
If the car is slowing down, a force must be pulling in the direction opposite to its velocity.
the angular speed of the hour hand of a clock in rad/s is
1/1800 pie
the angular speed of the minute hand of a clock in rad/s is
1/30 pie
when the center of a bicycle wheel has linear velocity vcm relative to the ground the velocity relative to the ground of point p at the top of the wheel is
2vcm
a uniform cylinder of radius r mass m and length l rotates freely about a horizontal axis parallel and tangent to the cylinder. the moment of inertia of the cylinder about this axis is
3/2mr2
a force f is applied toa cylindrical roll of paper of radius r and mass m by pulling on the paper as shown. the acceleration of the center of mass of the roll of paper is
4/3 f/m
a uniform sphere of radius r and mass m rotates freely about a horizontal xis that is tangent to an equatorial plane of the sphere the moment of inertia of the sphere about this axis is
7/5mr2
Consider the following controls in an automobile: gas pedal, brake, steering wheel. The controls in this list that cause an acceleration of the car are all three controls the gas pedal and the brake only the brake only the gas pedal
A. Because acceleration occurs whenever the velocity changes in any way - with an increase or decrease in speed, a change in direction, or both - all three controls are accelerators. The gas pedal causes the car to speed up; the brake pedal causes the car to slow down. The steering wheel changes the direction of the velocity vector.
A dart is loaded into a spring-loaded toy dart gun by pushing the spring in by a distance d. For the next loading, the spring is compressed a distance 2d. How much work is required to load the second dart compared to that required to load the first? four times as much two times as much the same half as much one-forth as much
A. Because the work done in compressing a spring is proportional to the square of the compression distance x, doubling the value of x causes the work to increase four-fold.
An object experiences no acceleration. Which of the following cannot be true for the object? A single force acts on the object. No forces act on the object. Forces act on the object, but the forces cancel.
A. If a single force acts, this force constitutes the net force and there is an acceleration according to Newton's second law.
Which of the following is impossible for a car moving in a circular path? the car has tangential acceleration but no centripetal acceleration. the car has centripetal acceleration but no tangential acceleration. the car has both centripetal acceleration and tangential acceleration.
A. If the car is moving in a circular path, it must have centripetal acceleration given by Equation 4.15.
Which values represent the ball's vertical velocity and acceleration at points A, C, and E in the figure below? Vy = 0, ay = -9.80 m/s2 Vy = 0, ay = 9.80 m/s2 Vy = 0, ay = 0 Vy = -9.80 m/s2, ay = 0
A. Points A,C, and E all represent maximums on the graph. At these points, the ball is momentarily at rest (Vy = 0), but still accelerating at -g (ay = -9.80m/s2)
As the projectile in the figure below moves along its path, at what point are the velocity and acceleration vectors for the projectile parallel to each other? nowhere the highest point the launch point
A. The acceleration vector is always directed downward. The velocity vector is never vertical if the object follows a path such as that in the figure.
A baseball of mass m is thrown upward with some initial speed. A gravitational force is exerted on the ball at all points in its motion at all points in its motion, except at the highest point at no points in its motion
A. The gravitational force acts on the ball at all points in its trajectory.
You are riding on the Ferris wheel of question 1. What is the direction of the normal force exerted by the seat on you when you are at the top of the wheel? upward downward impossible to determine
A. The normal force is always perpendicular to the surface that applies the force. Because your car maintains its orientation at all points on the ride, the normal force is always upward.
An object falls off a table to the floor. We wish to analyze the situation in terms of kinetic and potential energy. In discussing the potential energy of the system, we identify the system as both the object and the Earth only the object only the Earth
A. We must include the Earth if we are going to work with gravitational potential energy.
Suppose you are running at constant velocity and you wish to throw a ball such that you will catch it as it comes back down. In what direction should you throw the ball relative to you? straight up at an angle to the ground that depends on your running speed in the forward direction
A. You should simply throw it straight up in the air. Because the ball is moving along with you, it will follow a parabolic trajectory with a horizontal component of velocity that is the same as yours.
If a fly collides with the windshield of a fast-moving bus, which object experiences the greater acceleration? the fly the bus the same acceleration is experienced by both
A. Because the fly has such a small mass, Newton's second law tells us that it undergoes a very large acceleration. The huge mass of the bus means that it more effectively resists any change in its motion and exhibits a small acceleration.
The gravitational force exerted by the Sun on the Earth holds the Earth in an orbit around the Sun. Let us assume that the orbit is perfectly circular. The work done by this gravitational force during a short time interval in which the Earth moves through a displacement in its orbital path is zero positive negative impossible to determine
A. The force does no work on the Earth because the force is pointed toward the center of the circle and is therefore perpendicular to the direction of the displacement.
Consider a block sliding over a horizontal surface with friction. Ignore any sound the sliding might make. If we consider the system to be the block and the surface, this system is isolated nonisolated impossible to determine
A. The friction force is internal to the system, so there are no interactions with the environment.
If vector B is added to vector A, under what condition does the resultant vector A + B have magnitude A + B? A and B are parallel and in the same direction. A and B are parallel and in opposite directions. A and B are perpendicular.
A. The magnitudes will add numerically only if the vectors are in the same direction.
Which of the following cannot possibly be accelerating? An object moving with a constant speed An object moving with a constant velocity An object moving along a curve
B. An object moving with constant velocity has Δv = 0, so, according to the definition of acceleration, a = Δv/Δt = 0. Choice (1) is not correct because a particle can move at a constant speed and change direction. This possibility also makes (3) an incorrect choice.
You place your physics book on a wooden board. You raise one end of the board so that the angle of the incline increases. Eventually, the book starts sliding on the board. If you maintain the angle of the board at this value, the book moves at constant speed speeds up slows down none of these
B. At the angle at which the book breaks free, the component of the gravitational force parallel to the board is approximately equal to the maximum static friction force. Because the kinetic coefficient of friction is smaller than the static coefficient, at this angle, the component of the gravitational force parallel to the board is larger than the kinetic friction force. Thus, there is a net downhill force parallel to the board and the book speeds up.
A dart is loaded into a spring-loaded toy dart gun by pushing the spring in by a distance d. For the next loading, the spring is compressed a distance 2d. How much faster does the second dart leave the gun compared to the first? four times as fast two times as fast the same half as fast one-fourth as fast
B. Because the work is proportional to the square of the compression distance x and the kinetic energy is proportional to the square of the speed v, doubling the compression distance doubles the speed.
Which of the following are vector quantities? your age, speed, mass acceleration, velocity the direction you are going your speed
B. For these quantities, the direction is necessary to specify the quantity completely. Choices A, C, and D are all scalar or directional. Acceleration and velocity are both values that have both direction and magnitude.
If at least one component of a vector is a positive number, the vector cannot have any component that is negative be zero have three dimensions
B. From the Pythagorean theorem, we see that the magnitude of a vector is nonzero if at least one component is nonzero.
You are riding on a Ferris wheel that is rotating with constant speed. The car in which you are riding always maintains its correct upward orientation - it does not invert. What is the direction of your centripetal acceleration when you are at the top of the wheel? upward downward impossible to determine
B. The centripetal acceleration is always toward the center of the circular path.
A crate is located in the center of a flatbed truck. The truck accelerates to the east, and the crate moves with it, not sliding at all. What is the direction of the friction force exerted by the truck on the crate? to the west to the east No friction force exists because the crate is not sliding.
B. The crate accelerates to the east. Because the only horizontal force acting on it is the force of static friction between its bottom surface and the truck bed, that force must also be directed to the east.
You press your physics textbook flat against a vertical wall with your hand. What is the direction of the friction force exerted by the wall on the book? downward upward out from the wall into the wall
B. The friction force acts opposite to the gravitational force on the book to keep the book in equilibrium. Because the gravitational force is downward, the friction force must be upward.
Consider a block sliding over a horizontal surface with friction. Ignore any sound the sliding might make. If we consider the system to be the block, this system is isolated nonisolated impossible to determine
B. The friction force represents an interaction with the environment of the block.
Consider a block sliding over a horizontal surface with friction. Ignore any sound the sliding might make. If we consider the system to be the surface, this system is isolated nonisolated impossible to determine
B. The friction force represents an interaction with the environment of the surface.
As a projectile thrown upward moves in its parabolic path, such as in the figure below, at what point along its path are the velocity and acceleration vectors for the projectile perpendicular to each other? nowhere the highest point the launch point
B. At only one point - the peak of the trajectory - are the velocity and acceleration vectors perpendicular to each other. The velocity vector is horizontal at that point and the acceleration vector is downward.
Suppose you are talking by interplanetary telephone to your friend, who lives on the Moon. He tells you that he has just won a newton of gold in a contest. Excitedly, you tell him that you entered the Earth version of the same contest and also won a newton of gold! Who is richer? You Your friend You are equally rich.
B. Because the value of g is smaller on the Moon than on the Earth, more mass of gold would be required to represent 1 newton of weight on the Moon. Thus, your friend on the Moon is richer, by about a factor of 6!
Choose the correct response to make the sentence true: A component of a vector is _____ larger than the magnitude of the vector. always never sometimes
B. From the Pythagorean theorem, the magnitude of a vector is always larger than the absolute value of each component, unless there is only one nonzero component, in which case the magnitude of the vector is equal to the absolute value of that component.
A passenger, observer A, in a car traveling at a constant horizontal velocity of magnitude 60 mi/h pours a cup of coffee for the tired driver. Observer B stands on the side of the road and watches the pouring process through the window of the car as it passes. Which observer(s) sees a parabolic path for the coffee as it moves through the air? A B both A and B neither A nor B
Both A and B Passenger A sees the coffee pouring in a "normal" parabolic path, just as if she were standing on the ground pouring it. The stationary observer B sees the coffee moving in a parabolic path that is extended horizontally due to the constant horizontal velocity of 60 mi/h.
Which of the following is true? If a car is traveling eastward, its acceleration is eastward. If a car is slowing down, its acceleration must be negative. A particle with constant acceleration can never stop and stay stopped.
C If a particle with constant acceleration stops and its acceleration remains constant, it must begin to move again in the opposite direction. If it did not, the acceleration would change from its original constant value to zero. Choice (1) is not correct because the direction of acceleration is not specified by the direction of the velocity. Choice (2) is also not correct by counterexample - a car moving in the -x direction and slowing down has a positive acceleration.
Under which of the following conditions is the magnitude of the average velocity of a particle moving in one dimension smaller than the average speed over some time interval? A particle moves in the + x direction without reversing. A particle moves in the - x direction without reversing. A particle moves in the + x direction and then reverses the direction of its motion. There are no conditions for which this is true.
C If the particle moves along a line without changing direction, the displacement and distance traveled over any time interval will be the same. As a result, the magnitude of the average velocity and the average speed will be the same. If the particle reverses direction, however, the displacement will be less than the distance traveled. In turn, the magnitude of the average velocity will be smaller than the average speed.
If a fly collides with the windshield of a fast-moving bus, which object experiences an impact force with a larger magnitude? the fly the bus the same force is experienced by both
C. In accordance with Newton's third law, the fly and bus experience forces that are equal in magnitude but opposite in direction.
An object experiences a net force and exhibits an acceleration in response. Which of the following statements is always true? The object moves in the direction of the force. The acceleration is in the same direction as the velocity. The acceleration is in the same direction as the force. The velocity of the object increases.
C. Newton's second law relates only the force and the acceleration. Direction of motion is part of an object's velocity, and force determines the direction of acceleration, not that of velocity.
A ball is connected to a light spring suspended vertically, as shown in the figure. When displaced downward from its equilibrium position and released, the ball oscillates up and down. In the system of the ball, the spring, and the Earth, what forms of energy are there during the motion? kinetic and elastic potential kinetic and gravitational potential kinetic, elastic potential, and gravitational potential elastic potential, and gravitational potential
C. The ball and the spring both contribute to elastic potential energy, and kinetic energy. Including the Earth in the system, the gravitational potential energy becomes internal and part of the motion.
Which of the following is the reaction force to the gravitational force acting on your body as you sit in your desk chair? The normal force exerted by the chair The force you exerted downward on the seat of the chair Neither of these forces
C. The reaction force to your weight is an upward gravitational force on the Earth due to you.
An object falls off a table to the floor. We wish to analyze the situation in terms of kinetic and potential energy. In discussing the kinetic energy of the system, we must include the kinetic energy of both the object and the Earth can ignore the kinetic energy of the Earth because it is not part of the system can ignore the kinetic energy of the Earth because it is so massive compared to the object
C. The reason that we can ignore the kinetic energy of the massive Earth is that this kinetic energy is so small as to be essentially zero.
The magnitudes of two vectors A and B are A = 12 units and B = 8 units. Which of the following pairs of numbers represents the largest and smallest possible values for the magnitude of the resultant vector R = A + B? 14.4 units, 4 units 12 units, 8 units 20 units, 4 units none of these answers
C. The resultant has its maximum magnitude A + B = 12 + 8 = 20 units when vector A is oriented in the same direction as vector B. The resultant vector has its minimum magnitude A - B = 12 - 8 = 4 units when vector A is oriented in the direction opposite vector B.
Choose the correct answer. The gravitational potential energy of a system is always positive is always negative can be negative or positive
C. The sign of the gravitational potential energy depends on your choice of zero configuration. If the two objects in the system are closer together than in the zero configuration, the potential energy is negative. If they are farther apart, the potential energy is positive.
In an isolated system, which of the following is a correct statement of the quantity that is conserved? kinetic energy potential energy kinetic energy plus potential energy both kinetic energy and potential energy
C. The total mechanical energy, kinetic plus potential, is conserved.
You are traveling along a freeway at 65 mi/h. Your car has kinetic energy. You suddenly skid to a stop because of congestion in traffic. Where is the kinetic energy that your car once had? All of it is in internal energy in the road. All of it is in internal energy in the tires. Some of it has transformed to internal energy and some of it transferred away by mechanical waves. All of it transferred away from your car by various mechanisms.
C. The brakes and the roadway are warmer, so their internal energy has increased. In addition, the sound of the skid represents transfer of energy away by mechanical waves.
Consider the passenger in the car making a left turn in the figure on the back of the card. Which of the following is correct about forces in the horizontal direction if the person is making contact with the right-hand door? The passenger is in equilibrium between real forces acting to the right and real forces acting to the left. The passenger is subject only to real forces acting to the right. The passenger is subject only to real forces acting to the left. None of these is true.
C. The only forces acting on the passenger are the contact force with the door and the friction force from the seat. Both of these are real forces and both act to the left in Figure 6.11. Fictitious forces should never be drawn in a force diagram.
Which of the following correctly describes the centripetal acceleration vector for a particle moving in a circular path? constant and always perpendicular to the velocity vector for the particle constant and always parallel to the velocity vector for the particle of constant magnitude and always perpendicular to the velocity vector for the particle of constant magnitude and always parallel to the velocity vector for the particle
C. We cannot choose (1) or (2) because the centripetal acceleration vector is not constant - it continuously changes in direction. Of the remaining choices, only (3) gives the correct perpendicular relationship between ac and v.
Which of the following statements is most correct? It is possible to have forces on an object in the absence of motion of the object. It is possible to no forces on an object in the presence of motion of the object. Neither (a) nor (b) is correct. Both (a) and (b) are correct.
D Choice (1) is true. Newton's first law tells us that motion requires no force: an object in motion continues to move at constant velocity in the absence of external forces. Choice (2) is also true. A stationary object can have several forces acting on it, but if the vector sum of all these external forces is zero, there is no net force and the object remains stationary.
After a ball is thrown upward and is in the air, its speed increases decreases increases and then decreases decreases and then increases remains the same
D. While the ball is rising, it is slowing down. After reaching the highest point, the ball begins to fall and its speed increases.
A particle moves in a circular path of radius r with speed v. It then increases its speed to 2v while traveling along the same circular path. The centripetal acceleration of the particle has changed by a factor of 0.25 0.5 2 4 impossible to determine
D. Because the centripetal acceleration is proportional to the square of the speed, doubling the speed increases the acceleration by a factor of 4.
A particle moves along a path and its speed increases with time. In which of the following cases are its acceleration and velocity vectors perpendicular everywhere along the path? the path is circular the path is straight the path is a parabola never
D. The velocity vector is tangent to the path. If the acceleration vector is to be perpendicular to the velocity vector, it must have no component tangent to the path. On the other hand, if the speed is changing, there must be a component of the acceleration tangent to the path. Thus, the velocity and acceleration vectors are never perpendicular in this situation. They can only be perpendicular if there is no change in the speed.
You are playing with your daughter in the snow. She sits on a sled and asks you to slide her across a flat, horizontal field. You have a choice of (1) pushing her from behind, by applying a force downward on her shoulders at 30° below the horizontal, or (2) attaching a rope to the front of the sled and pulling with a force at 30° above the horizontal. Which would be easier for you and why? #1, because the normal force between the sled and the snow is increased #1, because the friction force between the sled and the snow is decreased #2, because the normal force between the sled and the snow is increased #2, because the friction force between the sled and the snow is decreased
D. When pulling with the rope, there is a component of your applied force that is upward. This reduces the normal force between the sled and the snow. In turn, this reduces the friction force between the sled and the snow, making it easier to move. If you push from behind, with a force with a downward component, the normal force is larger, the friction force is larger, and the sled is harder to move.
You push an object, initially at rest, across a frictionless floor with a constant force for a time interval Δt, resulting in a final speed of v for the object. You repeat the experiment, but with a force that is twice as large. What time interval is now required to reach the same final speed v? 4Δt 2Δt Δt Δt/2 Δt/4
D. With twice the force, the object will experience twice the acceleration. Because the force is constant, the acceleration is constant, and the speed of the object (starting from rest) is given by v = at. With twice the acceleration, the object will arrive at speed v at half the time.
Which of the following statements is true about the relationship between A · B and (-A) · (-B)? A . B = -[(-A) . (-B)] If A · B = AB cos θ, then (-A) · (-B) = AB cos (θ+ 180°) Both (a) and (b) are true. Neither (a) nor (b) is true.
D. Answer (1) is incorrect because the scalar product (-A) · (-B) is equal to A · B. Answer (2) is incorrect because AB cos (θ + 180°) gives the negative of the correct value.
Which of the following statements is true about the relationship between the dot product of two vectors and the product of the magnitudes of the vectors? A . B is larger than AB. A . B is smaller than AB. A . B could be larger or smaller than AB, depending on the angle between the vectors. A . B could be equal to AB.
D. Because of the range of values of the cosine function, A · B has values that range from AB to -AB.
A ball is thrown upward. While the ball is in free fall, its acceleration increases decreases increases and then decreases decreases and then increases remains constant
E For the entire time interval that the ball is in free fall, the acceleration is that due to gravity.
An older model car accelerates from rest to speed v in 10 seconds. A newer, more powerful sports car accelerates from rest to 2v in the same time period. What is the ratio of the power of the newer car to that of the older car? 0.25 0.5 1 2 4
E. Because the speed is doubled, the kinetic energy is four times as large. This kinetic energy was attained for the newer car in the same time interval as the smaller kinetic energy for the older car, so the power is four times as large.
If A + B = 0, the corresponding components of the two vectors A and B must be equal positive negative of opposite sign
Each set of components, for example, the two x components Ax and Bx, must add to zero, so the components must be of opposite sign.
A rock of mass m is dropped to the ground from a height h. A second rock, with mass 2m, is dropped from the same height. When the second rock strikes the ground, its kinetic energy is twice that of the first rock four times that of the first rock the same as that of the first rock half as much as that of the first rock impossible to determine
The more massive rock has twice as much gravitational potential energy associated with it compared to the lighter rock. Because mechanical energy of an isolated system is conserved, the more massive rock will arrive at the ground with twice as much kinetic energy as the lighter rock.
A particle moves along a path and its speed increases with time. In which of the following cases are its acceleration and velocity vectors parallel? the path is circular the path is straight the path is a parabola never
The velocity vector is tangent to the path. If the acceleration vector is to be parallel to the velocity vector, it must also be tangent to the path. This requires that the acceleration vector have no component perpendicular to the path. If the path were to change direction, the acceleration vector would have a radial component, perpendicular to the path. Thus, the path must remain straight.
five objects of mass m move at velocity v at a distance r from an axis of rotation perpendicular to the page through point a the one that has zero angular momentum about that axis is
a without a circle in the middle with velocity going northeast
five identical cylinders are each acted on by forces of equal magnitude which force exerts the biggest torque
force going right or east
the diagram below shows five 20kg rods of the same 2m length free to totate about axes through the rods. which rod experiences the greatest gravitational torrque
axis at 2.0
when an object is effectively isolated from external torques like an ice skater twirling on the tip of one skate the angular momentum of the object
cannot be changed except by friction at the point of contact
stars originate as large bodies of slowly rotating gas, because of gravity these clumps of gas slowly decrease in size. the angular veolocity of a star increases as It shrinks becuase
conservation of angular momentum
two objects of mss m=2m and m=m move around a totation axis o in parallel cirlces of radii r=r and r2=2r with equal tangential speeds as they roate forces of equal magnitude are applied opposite to their velocities to stop them which statement is correct
m2 will stop first because its torque is greater
a hocket puck traveling at speed v on essentially frictionless ice collides elastically with one end of a straight stick lying flat on the ice. in the collison
momentum is conserved, angular momentum is conserved and energy is conserved all of the above are conserved
a campus bird spots a member of an opposing football team in an amusement park. the football player is on a ride whre he goes around at angular velocity w at distance r from the center. the bird flies in a horizontal circle above him. will a dropping the bird releases while flying directly above the person;s head hit him
no because it maintains the tangential velocity the bird had at the instand it started falling
a hockey puck traveling at speed v on essentially frictionless ice collides with one end of a straight stick lying flat on the ice and sticks to that end. in this collison
only momentum and angular momentum are conserved
a solid sphere spherical shell solid cylinder and acylindrical shell all have the same mass m and radius r if they are released from rest at the same elevation and roll without slipping whichreaches the bottom of an inclinded plane first
solid sphere
a rigid rod of length l rotates about an axis perpendicular to the rod, with one end of the rod fixed the the axis. which of the following are equal at all points of the rod
the angular position, the angular velocity, and the angular acceleration
when the sum of the external forces and the sum of th external torques on a body are both zero we can conclude that
the body may have constant linear or constant angular velocity or both simultaneously
two boys in a canoe toss a baseball back and forth. what effect will this have on the canoe. neglect velocity dependent frictional forces with water or air
the canoe will oscillate back and forth always moving opposite to the ball
when a wheel is rolling without slipping the magnitude of its velocity relative to the ground is greatest at
the point at the top o the wheel opposite to the point in contact with the ground
the diagram below shows five cylinders each cylinder rotating with constant angular velocity about its central axis. the magnitude of the tangential velocity of one point of each clylinder is hown along with each cylinders radius and mass, whichclyinder has the largest angular momentum
v 4 r 2 m20
two forces of magnitude 50n as shown in the figure below act on a cylinder of rdius 4m and mass 6.25kg. the cylinder which is initially at rest sits on a frictionless surface. after 1 second the velocity and angular velocity of the clinder in m/s and rad/s are respectivly
v=0 w=4
